This application is based on and claims priority to Japanese Patent Applications No.2000-173894, filed Jun. 9, 2000, No.2000-173903, filed Jun. 9, 2000, and No.2000-173928, filed Jun. 9, 2000, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates to a four-cycle engine for a marine drive, and more particularly relates to a four-cycle engine for a marine drive that includes a variable valve timing mechanism.
2. Description of Related Art
A typical outboard motor comprises a power head and a housing unit depending from the power head. The power head includes an internal combustion engine that drives a marine propulsion device such as a propeller with a driveshaft and a propulsion shaft that both are journaled within the housing unit. The marine propulsion device is attached to the end of the propulsion shaft extending out of the housing unit and is placed in a submerged position.
Recently, many outboard motors are powered by a four-cycle internal combustion engine because of the better emission control capability of four-cycle technology when compared to two-stroke technology. Generally, a four-cycle engine includes at least one intake port and at least one exhaust port that are in communication with a combustion chamber. One or more camshafts can be provided to actuate valves associated with the ports such that flow can be controlled through the ports. The valve movement is timed so that air can be introduced into the combustion chamber, compressed in the combustion chamber, combusted in the combustion chamber and the resulting exhaust gases then can be discharged from the combustion chamber.
Typical automobile engines include a variable valve timing mechanism that can advantageously change the timing of the opening and closing of the valves. Such variable valve timing mechanisms can adjust the timing of the valves such that a first valve timing is used at higher engine speeds and a second valve timing is used as low engine speeds. The valve timing usually is advanced in the high engine speed range to ensure high charging efficiency and high performance. Similarly, the valve timing can be delayed in the low engine speed to ensure high combustion efficiency, fuel economy and good emission control. Thus, generally speaking, the valve timing is adjusted to either an advanced first valve timing for higher engine speed ranges or a delayed second valve timing lower engine speed ranges.
Typically, adjusting the valve timing and configuring at least the intake system result in higher performance only in a particular desired power range. Because of this design characteristic, engine torque in a range of low and medium engine speed is likely to be neglected in favor of optimizing performance in a higher engine speed range.
While adjusting the valve timing of an automotive engine in this manner can satisfactorily improve the performance of the engine in a desired power range, such a technique does not readily transfer to marine applications. A marine drive, such as a propeller, accelerates quickly to a high speed rotation because of the low viscosity of water. Thus, a relatively large engine torque generally is necessary in the low and medium engine speed ranges. For instance, the sudden acceleration of a propeller from a slower rotation, or a standstill, to a suitable operating speed requires a very large engine torque.
A need therefore exists for an improved four-cycle engine for a marine drive that can generate relatively large torques while accelerating in low and medium engine speed ranges.
Another problem (i.e., over-revolution of the engine or xe2x80x9credlining the enginexe2x80x9d) may arise also with marine drives. Automobile engines usually cut the supply of fuel (i.e., interrupted fuel injection, for instance) when the engine is revved to a high enough speed. By cutting the fuel, then engine returns to a suitable rotational speed or a normal operating condition. This method of engine speed control, however, generally is not suitable for marine drives due to the relatively high loads incurred while the watercraft is moving. In other words, reducing the amount of fuel in the air-fuel mixture still allows a low energy power stroke, which can cause swings in the engine speed. If the fuel-cut method were used, the engine speed might abruptly lower such that relatively large fluctuations in the engine speed would result during the over-rev control.
Outboard engines, thus, generally employ another method in which ignitions are cut if the over-revving occurs. While the method is effective against over-rev situations, unburned fuel can be discharged to the atmosphere when the ignition is cut. If the engine includes a catalyst within the associated exhaust system, the unburned fuel can foul the catalyst under extreme conditions.
Another need thus exists for an improved four-cycle engine for a marine drive that can prevent over-revving from occurring without causing major fluctuations in engine speed.
Some engines for marine drives also employ an idle air delivery device that bypasses a throttle valve in a main intake passage. An idle valve is provided within the delivery device to measure an amount of idle air passing therethrough. Changing a position of the idle valve can control the idle speed of the associated motor. Although idle air is delivered to the combustion chamber through the idle air delivery device, the throttle valve desirably is slightly opened to allow a light air flow through the main intake passage such that the idle speed can be substantially stabilized. The light flow of air also works to prevent sticking of the throttle valve when higher engine speed operation is desired.
Under certain circumstances, the idle speed may unexpectedly and unintentionally increase. More specifically, because the poorly regulated light flow of air through the main intake passage, air amounts delivered to the combustion chamber during idle can vary such that idle speed can exceed a desired objective idle speed. In some applications, delaying ignition timing can reduce the effects of this problem. This solution, however, may decrease fuel economy as well.
Hence, a further need exists for an improved four-cycle engine for a marine drive that can substantially maintain an actual idle speed at an objective idle speed without unwarranted decreases in fuel economy.
In accordance with one aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body and a member movable relative to the engine body. The engine body and the member together define a variable-volume combustion chamber. An air induction device is arranged to introduce air to the combustion chamber with the air induction device comprising an intake port that provides a connection between the air induction device and the combustion chamber. An intake valve is movable relative to the intake port between an open position and closed position such that the intake valve can selectively inhibit air flow into the combustion chamber. A valve actuator is rotatably journaled relative to the engine body. The valve actuator moves the intake valve at a preset angular position of the valve actuator. A valve actuator driving arrangement is adjustably connected to the valve actuator such that the preset angular position can be advanced or delayed through movement relative to the valve actuator driving arrangement. A setting mechanism is interposed between the valve actuator driving arrangement and the valve actuator. The setting mechanism is arranged to adjust the preset angular position of the valve actuator relative to the valve actuator driving arrangement. The setting mechanism is capable of adjusting the valve actuator between a first limit angular position and a second limit angular position with the first limit angular position being advanced relative to the second limit angular position. A sensor is arranged to sense an amount of the air within the induction device and a control system is adapted to control the setting mechanism based upon the signal of the sensor. The control system is adapted to control the setting mechanism to set the valve actuator to an adjusted angular position that is advanced relative to a current angular position when the signal indicates that the amount of the air increases and a change rate of the amount is greater than a preset change rate.
In accordance with another aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body and a movable member movable relative to the engine body. An output shaft is rotatably driven by the movable member. The engine body and the movable member together define a combustion chamber. An air induction device is arranged to introduce air to the combustion chamber and the air induction device comprises an intake port communicating with the combustion chamber. An intake valve is adapted to selectively open and close the intake port. A valve actuator is journaled on the engine body for rotation to actuate the intake valve at a first angular position. A setting mechanism is arranged to adjust the valve actuator to an angular position between a first limit angular position and a second limit angular position with the first limit angular position being advanced relative to the second limit angular position. A sensor is arranged to sense a rotational speed of the output shaft and a control system is configured to control the setting mechanism based upon the signal of the sensor. The control system controls the setting mechanism to set the valve actuator to an angular position that is different from a present angular position when the signal of the second sensor indicates that the rotational speed of the output shaft is greater than a first preset speed.
In accordance with a further aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body and a movable member movable relative to the engine body. An output shaft is driven for rotation by the movable member. The engine body and the movable member together define a combustion chamber. An air induction device is arranged to introduce air to the combustion chamber. The air induction device defines an intake port into the combustion chamber and comprises a throttle valve movable between an open position and a closed position to measure a flow of air. An intake valve is movable to open and close the intake port. A valve actuator is journaled on the engine body for rotation to actuate the intake valve. A setting mechanism is arranged to set the valve actuator to an angular position between a first angular position and a second angular positions with the first angular position being advanced relative to the second angular position. A first sensor is arranged to sense a rotational speed of the output shaft and a second sensor is arranged to sense a position of the throttle valve between the open and closed positions. A control system is configured to control the setting mechanism based upon the respective signals of the first and second sensors. The control system controlling the setting mechanism to set the valve actuator to an angular position that is different from a present angular position when the signal of the second sensor indicates that the throttle valve is generally at the closed position and the signal of the first sensor indicates that the rotational speed of the output shaft is greater than a preset speed.
In accordance with a still further aspect of the present invention, an internal combustion engine for a marine drive comprises an engine body and a movable member movable relative to the engine body. The engine body and the movable member together define a combustion chamber. An air induction device is arranged to introduce air to the combustion chamber. The air induction device defines an intake port next to the combustion chamber. An intake valve is movable between open and closed positions of the intake port. A valve actuator is journaled on the engine body for rotation to actuate the intake valve at a set angular position. A setting mechanism is arranged to set the valve actuator to an angular position between a first angular position and a second angular positions. The first angular position is advanced relative to the second angular position. Means are provided for controlling the setting mechanism. The means controls the setting mechanism to set the valve actuator to an angular position that is closer to the first angular position than a present angular position when an operation of the engine is accelerated under a condition that an engine speed of the engine is less than a preset speed.
In accordance with a yet further aspect of the present invention, a method is provided for controlling an internal combustion engine having an intake valve arranged to admit air to a combustion chamber when opened, a valve actuator arranged to actuate the intake valve at a set angular position, a setting mechanism arranged to set the valve actuator at least between first and second angular positions, the first angular position being advanced relative to the second position, and at least one sensor and a control device. The method comprises determining whether the engine is under an acceleration condition based upon a signal of the sensor and controlling the setting mechanism to advance the valve actuator to an angular position that is closer to the first angular position than a present angular position by the control device when the acceleration condition is determined.
In accordance with a still another aspect of the present invention, a method is provided for controlling an internal combustion engine having an intake valve arranged to admit air to a combustion chamber when opened, a valve actuator arranged to actuate the intake valve at a set angular position, a setting mechanism arranged to set the valve actuator to an angular position between a first angular position and a second angular position, the first angular position being advanced relative the second position, at least one sensor, and a control device. The method comprises determining whether an engine speed is greater than a preset speed and controlling the setting mechanism to set the valve actuator to an angular position that is different from a present angular position when the engine speed is greater than the preset speed.
In accordance with a yet another aspect of the present invention, a method is provided for controlling an internal combustion engine having a throttle valve arranged to measure an amount of air, an intake valve arranged to admit the air to a combustion chamber when opened, a valve actuator arranged to actuate the intake valve at a set angular position, a setting mechanism arranged to set the valve actuator to an angular position between a first angular position and a second angular position, the first angular position being advanced relative to the second position, at least one sensor and a control device. The method comprises determining whether the throttle valve is generally in a closed position, determining whether an engine speed is greater than a preset speed and controlling the setting mechanism to set the valve actuator to an angular position that is different from a present angular position when the throttle valve is generally closed and the engine speed is greater than the preset speed.